This invention relates to visual displays comprising rotating hollow beads strung on strings and utilizing optical and electromagnetic anisotropy.
Electrophoresis and triboelectricity are both surface phenomena whereby electric charge is generated on a surface. The combination of electrophoreses and triboelectricity on the same surface enhances the generation and retention of charge over either acting alone. Magnetic anisotropy is established by means of a material that exhibits magnetic activity. For purposes of this invention the term `electromagnetic activity` will be used to describe activity attributable to either electric activity or magnetic activity acting alone or in combination. Visual anisotropy is achieved by the utilization of colored materials. Display elements are formed as hollow beads on a string or fiber and the beads may be cylindrical, spherical, or of some other shape. The beads are hollow in the sense that they include a central hole through the bead near an axis. The string serves to confine the beads during fabrication and remains an integral part of the resultant display device whereby fabrication is facilitated and mechanical robustness is achieved in the final product.
Triboelectricity is the production of electric charge by friction or contact between dissimilar materials. Friction or relative motion between the materials develops electric charge. Triboelectricity has been and is a key process in the xerographic industry. Toner articles dispersed through an array of capillaries receive electric charge by contact and/or friction as they transit the capillaries. Particles or materials that have acquired surface charge by triboelectricity are capable of being moved, positioned and oriented by an electric field. A novel application of this feature is the utilization of triboelectric materials that develop positive charge along with triboelectric materials that develop negative charge to create bipolar and/or multi-polar particles. The resultant particle is capable of orientation in an electric field. This feature has been described in my U.S. Pat. No. 5,940,054 "TRIBOELECTRIC ELECTRET", which is incorporated herein by reference.
Electrophoreses is an electrochemical process where by an electric charge is developed at a solid-liquid interface as a result of an electrokinetic potential, the zeta-potential. As a result of the induced surface charge a particle will exhibit mobility under the influence of an electrical field. This effect is the basis of liquid xerographic applications. There is experimental evidence that the charge on suspended particles deteriorate with time. In particular, negatively charged particles may lose their charge in a few hours or days.
An inventive application described herein utilizes particles having surface areas that are comprised of materials that exhibit both triboelectric and electrophoretic activity. Electrophoreses generates charge even in the absence of friction or relative motion. Triboelectric effects on the other hand generate charge by friction independent of the electrokinetic potential. In the case of electrophoreses by itself, any ions within the liquid medium will migrate to charged areas on the particles, degrading the charge. These ions can be removed and the charge replenished by triboelectricity. By the combined action of these two effects charge is developed and retained under a wider range of condition than available with either by itself.
Electrophoretic charge anisotropy is the basis for a number of display approaches that utilize bipolar particles. These included, among others, those described in U.S. Pat. No. 4,126,854 (1978), U.S. Pat. No. 4,261,653 (1981), and U.S. Pat. No. 5,751,268 (1998). These prior art systems in general utilize anisotropic microspheres in a fluid filled cavity in an elastomer that is thick relative to the cavities. Electrodes are not integral with the cavity. Drive voltages must be applied external to the elastomer. Because of the elastomer thickness drive voltages are, typically, several tens of volts. With electrophoreses alone a very high resistivity liquid is mandated, and the high resistivity must be maintained over the lifetime of the apparatus. There is no means to replenish charge lost due to ion migration within the liquid.
In the present invention a preferred approach utilizes hollow micro cylindrical elements as beads on a string and in a plurality of cavities wherein drive electrodes are included. These micro cylinders are produced as "beads-on-a-string" by drawing a glass fiber from a preform that is comprised of a number of glass strands and by subsequent processing. A selection of glasses are fused into a preform comprising a plurality of colored glasses fused into a tube around a soluble glass tube which is in turn fused to a relative inert glass core. The preform is heated and pulled into a fiber using well-known techniques. A fiber results which posses essentially the same cross section of glasses as the preform. State of the art methods allow the pulling very long fibers of clad glass having the extreme uniformity and the very small diameters needed to support single mode propagation of laser light.
Colored glass is the preferred material for the outer surface of the fiber. However, optionally, the outer surface of a fiber can be coated with dye dispersed within a suitable polymer to achieve a desired color or plurality of colors.
An optional glass component of the preform, and hence resultant fiber, comprises a glass having magnetic capabilities, for instance iron oxide interspersed in silicon dioxide. Following pulling into a fiber a magnetic polarization is established in the magnetizable glass by an external magnetic field. Exploiting the natural hysteresis of the iron oxide the induced magnetic polarization remains within the glass after the external field is removed.
Subsequent to the pulling the fiber, polymers having a combination of electrophoretic and triboelectric activity are applied to selected regions of the fiber surface. These polymers are selected to exhibit electric activity whereby the triboelectric and electrophoretic activities reinforce each other.
The fiber is next processed to achieve a string of hollow beads-on-a-string wherein each bead comprises a display element bead whereby one picture element is displayed. The multi colored outer region is cut into bead defining segments utilizing state-of-are-art methods. A photo-resist is applied to the fiber, optical exposure of a plurality of rings along the fiber defines the cylindrical elements, and the soluble resist is removed. The resulting rings of unprotected glass are then etched sufficiently deep to cut through the outer multi colored surface glass, but not deep enough to reach entirely through the to the central hard glass core. The uncut portions of the fiber maintain fiber integrity for subsequent processing. When, in a later step the soluble glass is finally dissolved the inert central core remains as string the plurality of multicolor bead segments are cut free to become orientable hollow beads-on-a-string. Each bead is a hollow cylinder comprised of segments of colored glass possessing triboelectric/electrophoretic coatings indexed to the glass colors. Each bead includes both optical and electric isotropy and will become a display element in the inventive display that is the subject of the present invention. The thread upon which the beads are strung is comprised of the uncut fiber core and serves to confine the beads throughout subsequent processing and remain with the beads in the final display device. Manipulation of the very large numbers of elements, which will comprise the display, is greatly facilitated by confining the beads to a string and by further confining the strings of beads to a loom.
Optionally, a smaller bead can be formed coaxially with a larger bead of the same length and occupying the same location on the string. The two coaxial beads at a common display element location allow a more expansive color palette. The two beads of the coaxial pair are oriented independently. Preferably one bead of the pair includes electric anisotropy and the other exhibits magnetic anisotropy. The two beads can, however, exhibit the same type anisotropy and be driven by electrodes or coils spaced sufficiently apart to assure independent action.
A preferred coaxial bead approach comprises a four-color optically transmissive outer bead that exhibits electric anisotropy and is positioned into one of four orientations by a pair of electrodes together with a two color optically reflective inner bead that exhibits magnetic activity and is positioned to one of two positions by a coil. If the four-color segments of the outer bead are composed of: Clear, Blue, Cyan and Magenta and the two color segments of the inner bead are composed of: White and Yellow then a full eight set of primary colors can be obtained. With the inner bead oriented for White the coaxial bead combination can display, White, Blue, Cyan, or Magenta depending upon the outer beads orientation. With the inner bead set for Yellow then the combination can display Yellow, Black, Green, or Red for the same four orientations of the outer bead. The same full eight-color set is available with two other color combinations. Clear must always be included on the outer bead and White always on the inner bead. Red, Yellow and Magenta on the outer bead with Cyan on the inner ad is one combination. Green, Cyan and Yellow on the outer bead with Magenta on the inner bead is the other combination.
In the language of the color industry, color GAMUT is thought of as the three-dimensional space that encompasses all of the colors reproducible by a given process. Color PALETTE are the available specific colors within the gamut.
Subsequent to the pulling of the glass preform into a fiber additional processing generates a plurality of the beads-on-a-string and integrates them into a display device.
A preferred manufacturing approach which facilitates manipulating the many thousands of beads involved is to first mount the fiber as pulled onto a frame or loom much as warp threads are mounted in a weaving process. Many of the process steps to achieve the desired string of-beads-on a-thread are performed while the said fibers are confined to this loom. Positional accuracy of elements of the resultant display device is assured, in part, by the precision to which the loom is machined, including fiber handling "V" grooves within which fibers rest within the loom. State of the art techniques are well known that allow machining over the required extent and to the required precision.
In a subsequent step in the fabrication process a plurality of strings of beads-on-a-thread is transferred from the loom to the display substrate. Cross strand fibers strung upon a separate tooling loom and orthogonal to the strings of beads-on-a-thread are utilized to maintain precision location and spacing of the beads on the strings of beads-on-a-thread during fabrication. Beadwork on looms is an ancient technology, practiced by many cultures. Of passing interest to the present case is the "Sable" beadwork that became famous in France in the 1600's, wherein embroidery was sewn with beads as fine as grains of sand strung on strands of hair.
Electronic drive circuits are also generated as strings of beads-on-a-string with one drive circuit for each display bead location. In a preferred approach a first set of strings comprising driver electronics as beads on a string are affixed to a first face of a thin substrate. A second set of strings, comprising display beads on a string is affixed to the the second face of the substrate. The two sets of strings are preferably mutually orthogonal. With mechanical bonds established between the two sets of strings at their intersections. Electrical connectivity between beads of driver electronics on one substrate face and display beads on the other substrate face is by means of connectivity vias between the two substrate faces by which drive signal is conducted from driver electronic circuits to drive electrodes within cavities containing the display beads. Fabricating the display device wherein the strings of beads on the two faces of the substrate are orthogonal to one other provides a robust assembly. Additionally, providing a mechanical attachment through the substrate between the strings at each intersection adds to the robustness. The resulting assembly then exhibits many of the features of a weaving of warp and weft threads. The two orthogonal sets of threads support each other while providing a measure of mechanical flexibility to the assembly.
The display face of the substrate is comprised of an array of shallow cavities that serve to loosely confine the display beads while allowing freedom to rotate as driven. Closure of the display is by means of a window that comprises an array of shallow cavities that match the cavities on the substrate. To establish a secure mechanical connection from the window to the substrate, cavity defining ridges on both the substrate and the window are bonded to the core fibers upon which the strings of display beads-on-a-string are strung. The window and the substrate are by this means mechanically bonded to each other through a connection to the core fibers upon which display beads are string.
Additional mechanical integrity is achieved by encapsulating the substrate along with driver electronics on the driver face of the substrate in a polymer. As a final fabrication step the internal volume is filled with electrophoretic active liquid and the assembly sealed.
Connectivity traces for signal, synchronization, and power are included on the driver face of the substrate and a signal jack is included in the said encapsulation. These connectivity traces on the driver face of the substrate serve the same purpose as metal traces on a circuit board. Drive signals are connected between the electrodes at each display element bead and its driver circuit by means of the connectivity vias through the substrate. As a result of both repulsive and attractive fields display beads are oriented to present a selected face to a viewer. Once positioned, friction and inertia will serve to maintain bead orientation after removal of the drive signal.
Providing silicon electronics for driving display elements is a major consideration in any flat panel display device, and is of ongoing concern in the industry. Silicon-on-glass is a desirable approach for many reasons. For the highest performance, however, silicon must be processed at temperatures that require most expensive fused silica. Fused silica is highly desirable as a substrate and methods are desirable which minimize the quantity of both silicon and fused silica. This desire is highly compatible with the volume and area requirements of the micro cylinder flat panel display device that is the subject of this present invention. A preferred approach is one similar to that described in my U.S. Pat. No. 6,127,725 "THIN FILM ELECTRONICS ON INSULTOR ON METAL", that issued Oct. 3, 2000. The above referenced patent is hereby incorporated in this present patent application by reference.
In a preferred approach the desired electronic drivers for the display device, particulate fused silica is first deposited in a pattern of thin layers of isolated islands on tungsten foil. The silica is subsequently fused into isolated patches of fused silica glass on the refractory metal foil. Advantage is taken of the fact that the softening temperature of tungsten is significantly above that needed to fuse the silica. Silicon is next deposited on the fused silica islands and processed into high quality silicon at temperatures that are compatible with both tungsten and fused silica. The required electronics are then developed within the silicon by well-known techniques. Advantage is taken of the fact that temperatures needed to process the silicon to achieve its maximum utility are below the operating range of both fused silica and tungsten. A two-dimensional array of isolated islands of silicon electronic circuits on flexible tungsten foil results. Individual circuits are separately testable before utilization in the display array. Circuits that test bad may be tagged and subsequently cut out of the foil. In a subsequent step a good circuit fills the empty spot. Refractory metal foils other than tungsten, such as tantalum are possible.
The tungsten foil containing the two-dimensional array of electronic circuits are integrated with a loom of matching support fibers. Each individual circuit is then cut free by a process that includes folding portions of the adjacent foil loosely around a support fiber. A batch process is utilized whereby an entire row of circuits are processed by a moving tool. As the tool moves over the surface of the loom the entire two-dimensional array of circuits are cut free and loosely attached to the support fibers. The driver electronics thus also become a series of beads-on-a-string on a loom. These circuits remain on the support fibers and with the support fibers become an integral part of the resultant display device. These support fibers are securely attached to the driver face of the substrate by an encapsulation.
The intended display is comprised of a thin molded substrate to which is integrated the anisotropic display elements on a first substrate face and the driver electronics on the second other face. To assure registration integrity the loom of driver elements is integrated with the display substrate while the display substrate is still attached to one half of the substrate wherein it is molded. An encapsulation then seals the drivers to the substrate and provides a robust and permanent subassembly of driver electronics integrated with the display substrate.
With the driver electronics thus assembled to the reverse face of the substrate, the micro-cylinder display elements comprising a loom of strings of display beads-on-a-string are integrated with the upper, or display, face of the substrate after the upper mold half is removed. Metalization for the driver electrodes, together with their interconnectivity vias is added by means of standard processes, utilizing photo resist, optical exposure and development. Mechanical integrity of the assembly during integration of the said strings of display beads is assured by the substrate encapsulation.
The string onto which the display beads are strung is comprised of the uncut central core fiber. During integration of the loom of strings of display beads-on-a-string to the upper substrate face, this central core fiber is made to contact with, and is cemented to, a plurality of ridges of the substrate that lies between rows and columns of display elements. Prior to integration the ridges are contacted with a surface coated with a curable resin which wets the contact surface of the core fiber. Upon curing each core fiber thus become bonded to the substrate along a ridgeline which runs between the rows of display beads. As the substrate has previously been bonded to the driver electronics beads-on-a-string by the encapsulation, the assembly thus becomes mechanically robust.
The inventive display is further comprised of a transparent window through which display beads are viewed. This window includes a plurality of ridges that define a plurality of shallow cavities within which display beads are disposed. Prior to integration of the cavity defining ridges will have been contacted with an adhesive. Upon integration of the window the ridges on both the window and the substrate, wetted with adhesive, contact the core fiber on which the display beads are strung. When the curable adhesive is cured a mechanical bond is established between the window and the substrate through the central support fiber cores upon which the strings of display beads-on-a-string are strung. The substrate has, in a prior step, been securely attached to electronic circuits comprised of electronics driver strings of beads-on-a-string by an encapsulation. By this means a secure mechanical assembly is achieved element by element over the extent of the display.
The loom frames upon which strings of display beads-on-a-string are strung as well as loom frames upon which spacing fibers are strung comprise production tools. They do not become part of the final display. Consequently the said looms can be manufactured with great precision even at great expense. The precision and integrity of these tooling frames become a prime determinant of registration accuracy of elements of the display device.
It is an object of this invention to provide a display device comprising an array of anisotropic display elements as beads-on-a-string. It is another object of this invention to provide a visual display device utilizing display elements that combine visual and electro-magnetic anisotropy. It is a further object of this invention to utilize a combination of electrophoretic and triboelectric effects to produce and maintain electric anisotropy in the elements of the display whereby the beneficial features of each effect supplement those of the other. It is yet another object of this invention to integrate magnetic anisotropy with electric anisotropy for enhanced color presentation. It is an additional object of this invention to provide integral driver electrodes within individual cavities whereby the anisotropic elements are positionable with the low voltages and currents typical of silicon electronic circuits. It is yet another object to provide a visual display capable of displaying electronic image material wherein ambient light provides the illumination and the power requirements of a self-luminous display are obviated. It is a further object of this invention to provide a technology capable of supporting monochrome displays, highlight color displays and full color displays. It is yet another object of this invention to provide manufacturing processes and procedures to enable cost effective production of the intended display device. It is a further object f this invention to provide displays having a range of resolutions and display elements from the lowest instrument need to the highest need for industry and entertainment.